Test fixes and improvements + recovery docs as bonus track

C++ tests:
* Unbroke tests;
* Cleaned up code;
* Removed obsolete comments;
* Removed `-m` flag for trivial memory leak test:
We should use valgrind for that one. Also `getrusage` do not work properly with `mmap`ed files;
* Added self-recovery test that turns on via `-R` flag;
* Improved `stat` test;
* Improved new `range` tests;
* Removed old `range` tests;
* Removed useless `-w` flag.

Eblob:
* Formatting fixes.

Recovery:
* Fixes and improvements for documentation.